Pressure sensor

ABSTRACT

A sensor includes a deformable membrane that deflects in response to a stimuli. The sensor further includes a capacitive element coupled to the deformable membrane. The capacitive element is disposed within an enclosed cavity of the sensor. The capacitive element changes capacitance in response to the deformable membrane deflecting. The capacitive element comprises a getter material for collecting gas molecules within the enclosed cavity.

REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation patent application and claimsthe benefit and priority to the U.S. patent application Ser. No.15/085,592, which was filed on Mar. 30, 2016. The U.S. patentapplication Ser. No. 15/085,592 is based on and claims priority andbenefit to European Patent Application Number 15 000 967.8, which wasfiled on Apr. 2, 2015. The U.S. patent application Ser. No. 15/085,592and the European Patent Application No. 15 000 967.8 are hereinincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a pressure sensor.

BACKGROUND OF THE INVENTION

Pressure sensors are known. Typically, a membrane is suspended over acavity and becomes deflected in response to pressure.

However, gas molecules outgassing from the pressure sensor itself, orgas molecules entering from outside may affect defined conditions e.g.in the cavity and impact the measurement.

SUMMARY OF THE INVENTION

A pressure sensor, particularly an absolute pressure sensor, has adeformable membrane deflecting in response to pressure applied. A first,stationary electrode is provided, and a second electrode which is atleast coupled to the deformable membrane. In case of pressure applied,the deformable membrane deflects and a distance between the first andthe second electrode changes. Such change in distance results in achange of a capacity between the first and the second electrode which ismeasured and is indicative of the pressure applied.

At least one of the first and the second electrode comprises a gettermaterial for collecting gas molecules. Preferably, only the first,stationary electrode comprises the getter material. In a differentembodiment, it is only the second electrode comprising the gettermaterial, and in a further embodiment, both electrodes comprise gettermaterial.

By such solution, no additional space is required for a separate getterarrangement. Hence, the one or more electrodes comprising the gettermaterial have a multi-fold function:

sensing a deflection of the membrane;

at the same time chemically binding, ad-or absorbing or otherwisecollecting gas molecules that otherwise would impair the measurement;

protecting any underlying conventional non-getter electrode material,and as such preventing such material from degrading processes such ascorrosion.

Additionally, the integration of the getter material into the electrodeis beneficial in that electrode structures are designed to bemanufactured by conventional processes, such as CMOS processes, suchthat the manufacturing of the getter can be integrated in standardprocesses, such as CMOS processes.

In a preferred embodiment, the membrane separates a cavity and a portopen to an outside of the pressure sensor via which port the pressure tobe measured is applied. In such arrangement, it is preferred that thefirst, stationary electrode is arranged inside the cavity e.g. at abottom thereof facing the deformable membrane. Under the assumption thatdetrimental gas molecules may enter the cavity, the getter material ofthe first electrode preferably is exposed to the cavity. The cavitypreferably is evacuated. In the following the getter material may keepthe cavity “clean” from gas molecules for maintaining qualitymeasurements.

The second electrode may be attached to the membrane and faces thecavity. Alternatively, the membrane may itself be electricallyconducting and act as second electrode. In case of the second electrodecomprising the getter material, the getter material may face the cavity.

Generally, the getter material is provided for chemically combining orad- or absorbing gas molecules that may disturb the measurement ofpressure. Such gas molecules may outgas from the pressure sensor itself,e.g. into the cavity of the pressure sensor if available. And/or gasmolecules may enter the cavity from the outside, e.g. through materialinterfaces of the pressure sensor.

The getter material preferably is a non-evaporable metal or anon-evaporable alloy. Hence, it is preferred to use a getter material insolid form, and preferably in form of a coating. The getter materialcomprises or preferably consists of one of titanium, platinum,zirconium, and ZrVFe. The getter material preferably is suited to ad- orabsorb or bind one or more of H, O2, N2, H2O. Preferably, the gettermaterial is not Al/Cu.

In case at least one of the electrodes comprises the getter material assuggested, space can be saved given that the electrodes are to beprovided anyway. Instead, an additional getter coating may consumesurface e.g. in the cavity of a pressure sensor which may lead to anincrease of the overall size of the pressure sensor, which is notdesired in particular when the pressure sensor is a pressure sensorintegrated on a semiconductor substrate, e.g. in combination withprocessing circuitry.

As to the arrangement of the electrode that comprises the gettermaterial, and as to the provision of the getter material in anelectrode, multiple variants are suggested:

First, the subject electrode may completely consist of the gettermaterial.

Second, the subject electrode comprises the getter material and inaddition a conducting material different to the getter material. Suchnon-getter material preferably may be a metal such as Al/Cu as presentin metal layers of a CMOS layer stack which may serve as a buildingblock for the subject electrode. Other materials for the first layer maybe W, Au, Poly-Si, doped Si, etc.

In an embodiment of the second variant, the subject electrode comprisesa first layer and a second layer which second layer is made from thegetter material which is deposited on the first layer. The first layercomprises conducting material different to the getter material, such asAl/Cu. The second layer may fully cover a top surface of the first layerin one embodiment, and leave side faces of the first layer exposed.Alternatively, the second layer may take the shape of a capencapsulating the first layer at its top and additionally at its sidefaces such that the first layer is disconnected from the volume tocollect the gas molecules from. Hence, materials can be used as firstlayer that may not have been used in the past in view of their degradingcharacteristics. Here, the getter coating may additionally protect thenon-getter electrode material.

In another embodiment of the second variant, the subject electrodecomprises a center portion and a ring portion around the center portion,all in the same plane. The ring portion is disconnected from the centerportion by means of a gap, whereas outside the gap there may be anelectrical connection between the center portion and the ring portion.This variant utilizes space best, e.g. in a cavity.

Both of the above embodiments can be applied simultaneously, i.e. thecenter portion and/or the ring portion may comprise the first and thesecond layer. In another embodiment, both the center and the ringportion consist of getter material. In embodiments where both the centerand the ring portion comprise getter material, a different gettermaterial may be applied to the ring portion than to the center portion.In a different embodiment, only one of the center portion and the ringportion consists of the getter material while the other portion consistsof the conducting non-getter material, such as Al—Cu.

In case of any combinations of getter and non-getter material, it ispreferred that the getter material is exposed to the volume to collectgas molecules from, e.g. the getter material faces the cavity in oneexample.

In a preferred embodiment of the present invention, slots are providedin the getter material of the subject electrode. The slots may e.g. havea width of less than 10 μm, and preferably between 1 μm and 3 μm.Provided that the electrode has a plane extension the slots are directedvertical through the getter material, i.e. orthogonal to the planeextension of the electrode. In the case of a layered electrode, it ispreferred that the slots reach into, and preferably through the firstlayer underneath the second layer of getter material. The slots serve asstress reducing means given that stress may be induced from thermalmanufacturing processes of the sensor as such, from the deposition ofthe subject electrode itself, or from the deposition of individuallayers of the subject electrode if any. The material of the electrodemay now expand into the slots in response to thermal impact withoutconverting into significant stress. In addition, in particular in thetwo layer embodiment of the subject electrode, delamination effects ofthe two layers may be reduced by means of the slots.

In the case of a two portion electrode, slots may be applied to anygetter material irrespective in which portion the getter material isarranged. Preferably, in case one of the portions consisting only of aconducting material different to the getter material, this portion isnot provided with slots.

In a different preferred embodiment of the present invention, thesubject electrode comprises multiple individual elements of the gettermaterial, e.g. in the form of posts or pillars. Such individual elementsmay be arranged next to each other in a plane. Hence, the individualelements are disconnected from each other, e.g. by grooves. In case of alayered set-up of the elements, each individual element may comprise thefirst layer of conducting non-getter material and the second layer ofthe getter material deposited on the first layer. The grooves reachthrough both the first and the second layer.

As with the slots, the provision of the individual elements separatedfrom each other by the grooves reduces stress and delamination. Thematerial of the individual elements may now expand into the grooves inresponse to thermal impact without generating significant stress.

In one embodiment, the individual elements are disconnected from eachother except for electrically conducting bridges between two neighboringindividual elements. In a different embodiment, the connection may bemade within the CMOS layer stack “underneath” the posts in case theindividual elements are arranged on top of a CMOS layer stack. It ispreferred that each individual element is electrically connected to atleast one of the neighboring individual elements, in order to contactthe multitude of individual elements forming the electrode by only onecontact. In another variant, an individual element may be connected toall of its neighboring elements.

In a preferred embodiment of the pressure sensor, a cavity of thepressure sensor preferably is formed in a cap which cap preferably isattached to a first substrate such that the deformable membrane facesthe first substrate and such that a gap is provided between thedeformable membrane and the first substrate. The cap may further containa processing circuit. A deformation of the deformable membrane iscapacitively measured and converted into a signal that is supplied toand processed by the processing circuit in the cap. The first substratecontains a support portion to which the cap is attached. A contactportion of the first substrate is provided for electrically connectingthe pressure sensor to the outside world. The support portion issuspended from the contact portion by one or more suspension elements.In this arrangement, the deformable membrane as element sensitive tostress in essence is mechanically decoupled from the contact portion ofthe first substrate via which stress may be induced from an externalcarrier, or during mounting of the pressure sensor to an externalcarrier given that the contact portion preferably is the only portionvia which the pressure sensor is electrically and mechanically connectedto the external carrier. Not only is the deformable membrane no longerattached to the first substrate and is integrated into the cap instead.Moreover, already a first substrate portion, i.e. the support portion ismechanically decoupled from the contact portion. On the other hand, thecap is attached, and preferably is solely attached to the supportportion of the first substrate but not to the contact portion such thatthe membrane has no direct mechanical link to the contact portion of thefirst substrate. Hence, any propagation of stress induced via thecontact portion of the first substrate towards the membrane issignificantly reduced. In a preferred embodiment, the cap is at leastpartly manufactured from a second substrate. Preferably, the secondsubstrate is a semiconductor substrate, such as a silicon substrate.Hence, the second substrate may, for example, contain a bulk materialmade from silicon and various layers stacked on the bulk material suchas one or more of metal layers, insulation layers and passivationlayers. It is preferred, that the processing circuit is integrated intothe second substrate. And it is preferred that the cavity is formedsolely in the layer stack of the second substrate and does not reachinto the bulk material. In a preferred embodiment, the deformablemembrane is built from a third substrate, which is attached to the toplayer of the second substrate. The third substrate may, for example, bean SOI (Silicon On Insulator) substrate, wherein specifically thedeformable membrane may be built from a silicon layer of the SOIsubstrate while an insulation layer and bulk material of the SOIsubstrate are removed during processing. In the first substrate, thecontact and the support portion are preferably built by applying one ormore grooves vertically through the first substrate. By way ofmanufacturing the one or more grooves, one or more small portions of thefirst substrate remain for mechanically linking the support portion tothe contact portion. This/these small portion/s act as suspensionelement/s for suspending the support portion from the contact portion.Preferably, the one or more grooves are arranged vertically in the firstsubstrate, i.e. orthogonal to a plane extension of the first substrate.The suspension element/s may contain ridges, e.g. four ridges that holdthe support portion. Preferably, each suspension element is formedintegrally with the support portion and the contact portion given thatin a preferred embodiment the support portion, the contact portion andthe one or more suspension elements are built from the first substrate.In a preferred embodiment, the suspension elements do not represent theshortest path between the contact portion and the support portion but dohave a shape that allows one or more of a deflection or a rotation ofthe support portion relative to the contact portion, e.g. a deflectionin at least one direction of the plane of the first substrate. In suchway, translational and/or rotational forces applied to the supportportion via the cap may be dampened. The suspension elements may containspring portions for this purpose. Preferably, the deformable membraneitself serves as second electrode and as such contains electricallyconducting material. In one embodiment, the second electrode may be ametal layer, or in another embodiment, may be a polysilicon layer. Onthe other hand, the first electrode which contains the getter materialmay be arranged near or in the cavity at a stationary position such thatthis electrode arrangement may allow sensing a capacitance between thefirst electrode and the deflectable membrane which capacitance isdependent on the distance between the electrodes. For electricallyconnecting the cap to the first substrate, electrical connections may beprovided between the cap and the first substrate, e.g. in form of solderbumps or balls, or other electrically conducting elements that at thesame time may also serve as spacer elements for providing the gapbetween the first substrate and the deformable membrane. In order toconnect to the electrically conducting layers in the second substrate,contact windows may be provided into the second substrate and ifapplicable through the third substrate. On the other hand, the spacerelements may connect to contact pads on the first substrate which may beareas of conducting layers revealed from the first substrate.

Other advantageous embodiments are listed in the dependent claims aswell as in the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, aspects and advantages will becomeapparent from the following detailed description thereof. Suchdescription makes reference to the annexed drawings, wherein the figuresshow:

FIG. 1 a pressure sensor in a sectional view, according to an embodimentof the present invention;

FIGS. 2 to 4 in each, a cutout of a pressure sensor in a sectional view,according to an embodiment of the present invention;

FIGS. 5 to 7 in each, a top view on an electrode of a pressure sensor,according to an embodiment of the present invention;

FIG. 8 a cut along line A-A′ of FIG. 6;

FIG. 9 a cut along line B-B′ of FIG. 7;

FIG. 10 a zoom-in of area C of FIG. 7, according to a first embodimentof the present invention;

FIG. 11 a zoom-in of area C of FIG. 7, according to a second embodimentof the present invention;

FIG. 12 a sectional view of a pressure sensor according to an embodimentof the present invention;

FIG. 13 a bottom view of the first substrate 1 of the pressure sensor ofFIG. 12, according to an embodiment of the present invention; and

FIGS. 14 to 21 in each, a pressure sensor according to an embodiment ofthe present invention, in diagram a) in a cross section, and in diagramb) a top view on the corresponding first electrode.

DETAILED DESCRIPTION OF THE DRAWINGS

The term “pressure sensor” as used herein designates any type of sensormeasuring a parameter that is equal to or derived from the pressure of afluid, which fluid shall include a gas and a liquid. In particular, theterm designates relative (i.e. differential) as well as absolutepressure sensors, it also covers static as well as dynamic pressuresensors. Typical examples of applications of such sensors are e.g. inscientific instrumentation, meteorology, altitude measurement, soundrecording, mobile or portable computers and phones etc.

FIG. 1 illustrates a pressure sensor in a schematic sectional viewaccording to an embodiment of the present invention. The pressure sensorpreferably is an integrated pressure sensor, i.e. embodied by means of asubstrate, and preferably by a semiconductor substrate such as a siliconsubstrate, preferably together with a processing circuit (not shown) forat least preprocessing a pressure signal. The pressure sensor comprisesa body, which preferably contains a substrate 2, and a deformablemembrane 42 spanning a cavity 41 manufactured in the body. Thedeformable membrane 42 preferably deflects in response to pressureapplied to it, such as pressure of the surrounding air, which deflectionis in z-direction orthogonal to a plane extension of the pressure sensorin x-/y direction. The deflection of the membrane 42 is determined by acapacitive measurement. For this purpose, a first electrode 43 isarranged inside the cavity 41, e.g. at a bottom of the cavity 41, whilea second electrode 44 is arranged at or embodied in the membrane 42. Achange of a distance d between the first and the second electrode 43 and44 results in a change in the capacitance between the two electrodes 43and 44 which is measured by the electrodes 43 and 44. A correspondingsignal preferably is supplied to a processing circuit, e.g. integratedtogether with the sensor in the same chip. Preferably, the cavity 41 isevacuated, such that the pressure sensor is adapted to measure anabsolute pressure. One or both of the electrodes 43 and 44 comprise, orare made of a getter material. In the present example, it is assumedthat only the first, stationary electrode 43 comprises the gettermaterial.

FIGS. 2 to 4 each shows a cutout of a pressure sensor according to anembodiment of the present invention in a sectional view, e.g. a cutoutof the first electrode 43 of the pressure sensor of FIG. 1. In thepressure sensor of each of the FIGS. 2 to 4, it is assumed that thefirst electrode 43 is arranged on a stack of material layers, e.g. CMOSlayers, which at least include an insulating layer 248 arranged on asemiconductor bulk material 23, and a passivation layer 247 arranged onthe insulating layer 248. Preferably, the insulating layer 248 is a SiO2layer, while the passivation layer 247 is a SiNx layer. The firstelectrode 43 is arranged on the passivation layer 247. The layerstack—which may contain additional insulating and metal layers—and thebulk material 23 preferably contribute to the body of the pressuresensor.

In the embodiment of FIG. 2, the first electrode 43 is solely made froma getter material, e.g. from titanium. The getter material may insteadbe—and without being limited to the present embodiment—e.g. platinum, orzirconium. In the present embodiment, the getter material is depositedstraight on the passivation layer 247.

In the embodiment of FIG. 3, the first electrode 43 is layered.Presently, it contains a first layer 431 and a second layer 432. Thesecond layer 432 is made from the getter material. The first layer 431is from an electrode material, e.g. from a metal or an alloy differentto the getter material, and specifically from aluminum, and preferablyfrom aluminum containing a small amount of copper, i.e. the metalcomposition of a conducting layer of the material stack in the CMOSprocess. In the present embodiment, the first layer 431 is depositedstraight on the passivation layer 247, and the getter material isdeposited on the first layer 431.

The embodiment of FIG. 4 differs from the one of FIG. 3 in that thesecond layer 432 of getter material is formed as a cap separating thefirst layer 431 from the cavity. In this example, the first layer 413 isnot exposed at all to any molecules to be caught by the getter material,and therefore is fully protected from corrosion.

FIGS. 5 to 7 each show a top view on an electrode of a pressure sensor,according to an embodiment of the present invention. For example, theelectrode may be the first electrode 43, 432 and arranged as stationaryelectrode in the cavity of a pressure sensor, and specifically arrangedat the bottom of such cavity. In the present example, the firstelectrode 43 is of circular shape.

In the embodiment of FIG. 5, the getter material 43 or 432 is appliedcontinuous within the circumference of the first electrode 43.

In the embodiment of FIG. 6, slots 433 are provided in the gettermaterial 432. In a first embodiment, a hard mask may be providedrepresenting the slots in form of ridges which hard mask may be arrangedon the passivation layer, or more generally, on the place to build thegetter electrode at. The non-getter material if any, and the gettermaterial may be coated or vapor deposited between the ridges of the hardmask. In a different embodiment, the non-getter material if any, and thegetter material 43, 432 may be deposited as a continuous layer, andslots 433 may be applied afterwards, e.g. by etching or other processingmeans.

FIG. 8 is a cut along line A-A′ of the first electrode 43 of FIG. 6. Inthe present example, the first electrode 43 comprises two layers 431 and432, e.g. an Al/Cu layer 431, and the getter layer 432, e.g. made fromtitanium. As can be seen from FIG. 8, the slots 433 fully reach throughboth layers 431 and 432.

In the embodiment of FIG. 7, the first electrode 43 is made fromindividual elements 434 represented by small squares each. The elements434 are electrically connected with each other. Each element 434 atleast is electrically connected to one other element 434 in order toinsure the electrical connectivity of the overall first electrode 43.Preferably, an element 434 is electrically connected via an electricallyconducting bridge to at least one of the neighboring elements 434, andpreferably to all of the neighboring elements 434 as is shown in FIG. 10which is a zoom-in of area C of FIG. 7 in top view. Nine elements 434are zoomed wherein each of these elements 434 is connected to each ofthe neighboring elements 434 by means of V-shaped bridges 435 which inaddition act as springs. FIG. 11 shows the zoom-in of area C of FIG. 7according to a second embodiment of the present invention. Here, theindividual elements 44 are connected with each other via bridges 435that are shaped different than the bridges of FIG. 10. Again, thebridges 435 also act as springs.

FIG. 9 is a cut along line B-B′ of FIG. 7. In the present example, theelectrode 43 comprises two layers 431 and 432, e.g. an Al/Cu layer 431,and the getter layer 432, e.g. made from titanium. As can be seen fromFIG. 10 or FIG. 11, the individual elements 434 are separated from eachother except for the electrically conducting bridges 435. The bridges435 serve for electrically connecting all individual elements 434, suchthat the entire electrode 43 requires only a single electrical contact.

As to the manufacturing of the individual elements 434, in a firstembodiment a hard mask may be provided in form of a grid which hard maskmay be arranged on the passivation layer, or more generally, on theplace to build the getter electrode at. The non-getter material if any,and getter material may be coated or vapor deposited into the openingsof the grid. In a different embodiment, the non-getter material if any,and the getter material 432 may be deposited both as a continuous layer,and may be separated into individual elements 434 afterwards, e.g. byetching or other processing means.

FIG. 12 shows a schematic sectional view of a pressure sensor inaccordance with an embodiment of the present invention. The pressuresensor as shown is flipped with its solder balls 18 showing upwardswhile the pressure sensor will be mounted to a carrier with its solderballs 18 sitting on the carrier. The pressure sensor includes a firstsubstrate 1 and a cap 4 for the first substrate 1. The cap 4 preferablyis made from a second substrate 2 and a third substrate 3. The secondsubstrate 2 preferably is a semiconductor substrate, preferably asilicon substrate, and has a front side 21 and a backside 22. The secondsubstrate 2 contains a bulk material 23 of, e.g. silicon and a stack oflayers 24 on the bulk material 23. These layers 24 may be arranged forCMOS processing of the second substrate 2, and as such may also bedenoted as CMOS layers or material layers. Specifically, the layers 24can include for example a plurality of SiO2 layers, metal or polysiliconlayers. The bulk material 23 may contain doped regions within thesilicon such as indicated by the reference sign 241. These componentscan form active circuitry, such as amplifiers, A/D converters or otheranalog and/or digital signal processing units. A top layer 246 of thestack of layers 24 may be a dielectric layer of silicon oxide and/orsilicon nitride protecting the structures below it. In the presentexample, it is assumed that a processing circuit collectively referredto as 241 is integrated on the front side 21 of the second substrate 2by means of CMOS processing.

In the cap 4, a cavity 41 is formed by omitting or removing materialfrom one or more of the layers 24, presently the top layer 246. Thecavity 41 is closed by a deformable membrane 42. The membrane 42 issufficiently thin such that it deforms depending on a pressure dropbetween a pressure at the top of the membrane 42 and below it. A metallayer of the layer stack 24 may be used as a first stationary electrode43, and as such may be arranged at the bottom of the cavity 41. Thefirst stationary electrode 43 is entirely made from a getter material inthis embodiment.

The membrane 42 preferably is formed by a doped, conducting siliconlayer, is arranged as a sealing lid over the cavity 41, and may be usedas a second electrode 44 for which reason the deformable membrane 42 maycontain electrically conducting material. Hence upon a change inpressure the membrane 42 deflects and as such a distance between the twoelectrodes 43 and 44 changes which results in a change of thecapacitance between the two electrodes 43 and 44.

In the present example, the deformable membrane 42 is built from a thirdsubstrate 3. The third substrate 3 as shown in FIG. 12 may be theremainder of an SOI substrate, specifically its device layer after somemanufacturing steps. The third substrate 3 not only may contribute tothe deformable membrane 42. The third substrate 3 may contain contactwindows 244 reaching through which may also reach into one or more ofthe layers 24.

Corresponding signals may be transmitted from the electrodes 43 and 44via electrical paths 242 to the processing circuit 241 where thesesignals are processed. Signals processed by the processing circuit 241may be supplied to the first substrate 1.

The first substrate 1 may be a semiconductor substrate, e.g. a siliconsubstrate, or a glass substrate, for example, with a front side 11 and aback side 12. The semiconductor substrate 1 includes bulk material 13such as silicon, and one or more layers 14, such as an oxide layer onthe bulk material 13. The one or more layers 14 may further include forexample a plurality of SiO2 layers, metal or polysilicon layers.

The first substrate 1 contains vias 15 reaching vertically through thefirst substrate 1. Those vias 15 provide for an electrical connectionfrom the front side 11 of the substrate 1 to its backside 12. Those vias15 are manufactured by etching or drilling holes into the firstsubstrate 1 from its backside 12, by applying an oxide 151 to the hole,and by applying conducting material 152 to the oxide 151. At the backside 12 of the first substrate 1, the vias 15 are electrically connectedto contact pads 16 residing on an oxide layer 17 applied to the bulkmaterial 13, which contact pads 16 serve as support for solder balls 18or other contact means for electrically connecting the pressure sensorto the outside world, i.e. to another device. Alternative to the vias 15and the solder balls 18, there may be other ways of interconnecting thepressure sensor to the outside world, e.g. by means of wire bonds, bondpads or conducting structures that lead from the front side 11 of thefirst substrate 1 along its sides to the backside 12. The electricalconnection to the outside world may also be implemented via one or moreof a Land Grid Array, a Pin Grid Array, or a leadframe.

The assembly containing the second and the third substrate 2, 3 isattached to the front side 11 of the first substrate 1. The attachmentmay include bonding or other fusion techniques. In the present example,spacer elements 5 are provided between the third substrate 3 and thefirst substrate 1. The spacer elements 5 may have different functions:On the one hand, the spacer elements 5 provide for a gap 6 between thedeformable membrane 42 and the first substrate 1 which is required forsupplying the pressure medium to the membrane 42. On the other hand,some of the spacer elements 5, but not necessarily all may beelectrically conductive for connecting the contact windows 244 to thefirst substrate 1. Other or the same spacer elements 5 may providemechanical stability for the stacking of substrates 1, 3, and/or mayprovide mechanical protection to the inside of the pressure sensor, andspecifically to the membrane 42. For this purpose, it may be preferred,that a spacer element 51 is arranged in from of a ring at the edges ofthe substrates 1,3 providing mechanical stability, protection as well asan electrical connection, while spacer elements 52 are ratherpillar-like and provide electrical connections.

The signals provided by the processing circuit 241 hence may betransferred via one or more of the electrical paths 242 and via one ormore of the contact windows 244 to one or more of the spacer elements 5.As shown in FIG. 12, the spacer elements 52 end at the vias 15 of thefirst substrate 1 and are electrically connected thereto. Hence, thesignals are conducted through the vias 15 to the contact pads 16 and thesolder balls 18.

The first substrate 1 contains a support portion 7 and a contact portion8. Suspension elements not shown in the present illustration areprovided for suspending the support portion 7 from the contact portion8. The support portion 7 preferably encircles the contact portion 8 in aplane of the first substrate 1.

The contact portion 8 is separated from the support portion 7 by one ormore grooves 10. Owed to the manufacturing of the contact portion 8 andthe support portion 7 from the common first substrate 1, both portionsmay include bulk material 13 from the first substrate 1.

The cap 4 preferably is exclusively attached to the support portion 7 ofthe first substrate 1 via the spacer elements 5. On the other hand, itis preferred that it is solely the contact portion that provides amechanical and electrical contact to the outside world. Hence, theportion of the pressure sensor via which mechanical stress is induced,i.e. the contact portion 8 is mechanically decoupled from the rest ofthe pressure sensor and specifically from the deformable membrane 42 byway of the suspension elements.

A port for conducting a medium to the deformable membrane 42 in thepresent example encompasses the grooves 10 and the gap 6, or at leastparts of.

The overall height of the pressure sensor in the present example isabout 400 μm.

FIG. 13 illustrates a bottom view onto the first substrate 1 of thepressure sensor of FIG. 12. The first substrate 1 contains a supportportion 7 and a contact portion 8 wherein the support portion 7 issuspended from the contact portion 8 by means of a suspension element 9,which is a representation of a mechanical link between the two portions7 and 8. A groove 10 is arranged vertically through the first substrate1. Vias 15 are arranged in the support portion 7, while the solder balls18 are arranged in the contact portion 8. The contact portion 8 iselectrically connected to the support portion 7 by means of electricallyconducting structures such as the contact pads 16 which electricallyconducting structures may in generally be denoted as redistributionlayer.

FIGS. 14 to 21 each shows a pressure sensor according to an embodimentof the present invention, in diagram b) in a cross section, and indiagram b) in a top view on the corresponding first electrode 43. Forthe present embodiments, it is assumed that the pressure sensor maycontain a structural set-up identical or similar to the embodimentsshown in FIG. 1 or 12. Hence, a cavity 41 is formed by means of amembrane 42 facing a substrate containing silicon as bulk material 23and a stack of layers on top of the bulk material 23. In a top mostlayer 246, which presently may be an oxide layer such as a SiO2 layer, arecess is built for forming the cavity 41. The top most layer 246 may bearranged on a passivation layer 247, such as a SiNx layer which in turnis arranged on an oxide layer 248. Other layers, such as further CMOSlayers may be present in the stack of layers. In all the presentexamples, a first electrode 43 is arranged at a bottom of the cavity 41,while a second electrode not further shown may be integrated, arrangedon or otherwise coupled to the deflectable membrane 42. Contact windows244 are arranged in the top most layer 246 and the anchorage of themembrane 42.

In FIG. 14, the first electrode 43 comprises a center portion 436including a stack of a first layer 431 of electrically conductingmaterial, specifically a non-getter material, such as Al—Cu, which maybe made from a metal layer of the CMOS layer stack and of a second layer432 arranged on top of the first layer 431 and covering a top surface ofthe first layer 431 entirely. The second layer 432 is a continuous filmas can be derived from diagram 14 a). Outside the layered center portion436 and separated by a gap, the first electrode 43 further comprises aring portion 437 of getter material which is directly applied to thepassivation layer 247 or another layer of the stack of layers. This ringportion 437 lacks the first layer material 431 underneath. By suchmeans, the surface of the getter material can be enhanced, therebyimproving the capacitance of catching gas molecules. As can be derivedfrom diagram 14 a), an electrical contact 438 is provided for contactingthe ring portion 436 which ring portion 436 on the other hand iselectrically connected to the layered portion 436 (not shown). Suchconnection may be e.g. implemented by means of a metal layer in thestack of layers underneath the ring portion and the layered portion.Hence, in an embodiment of the present invention, the first electrode 43comprising the getter material is split into a central portion 436 and aring portion around 437 the center portion, wherein the center portion436 is a layered while the ring portion 437 is non-layered. Preferably,the first electrode 43 is arranged centered in the cavity 41, andpreferably at the bottom of the cavity 41.

The first electrode 43 in FIG. 15 solely comprises the centered, layeredportion 436 of the first electrode 43 of FIG. 14. Hence, a stack isprovided comprising a first layer 431 of electrically conductingnon-getter material, such as Al—Cu, and a second layer 432 comprisingthe getter material arranged on top of the first layer 431 and coveringa top surface of the first layer 431 entirely. Again, the second layer432 is a continuous film as can be derived from diagram 15 a).

The first electrode 43 in FIG. 16 solely comprises getter material inthe ring portion 437 of the first electrode 43 of FIG. 14. Instead, thecenter portion 436 is not layered, and only the first layer 431containing non-getter material is provided in the center portion 436.Again, it is assumed that the electrical contact 438 reaches via thering portion 436 to the first layer 431 which is not shown in the topview of diagram 16 a) which diagrams a) only indicate any gettermaterial in top view.

The first electrodes 43 in FIGS. 17 to 19 comprise slotted gettermaterial portions. The first electrode 43 of FIG. 17 resembles the firstelectrode 43 of FIG. 14 and as such comprises a layered center portion436 and a ring portion 437 around the center portion 436. However, boththe layered center portion 436 and the ring portion 437 comprise slots433 in the getter material as introduced in connection with theembodiment of FIG. 6. In the ring portion 437 as well as in the centerportion 436, the slots 433 reach through the getter material and throughthe first layer 431. In a different embodiment, the slots 433 reach onlythrough the getter material but not through the first layer 431.

The first electrode 43 in FIG. 18 solely comprises the layered centerportion 436 of the first electrode 43 of FIG. 17. Hence, a stack of afirst layer 431 of electrically conducting non-getter material, such asAl—Cu, and of a second layer 432 comprising the getter material ismanufactured. Again, the second layer 432 is slotted, and the firstlayer 431 preferably is slotted, too.

The first electrode 43 in FIG. 19 solely comprises getter material inthe ring portion 437 of the first electrode 43 of FIG. 17. The centerportion 436 is not layered and only comprises the first layer 431containing non-getter material. Again, it is assumed that the electricalcontact 438 reaches via the ring portion 437 to the first layer 431. Thering portion 437 comprises slots 433.

The first electrode 43 in FIG. 20 resembles the first electrode 43 ofFIG. 14. However, the second layer 432 of the center portion 436additionally covers the sides of the first layer 431 and hence forms acap for the first layer 431 such that the first layer 431 is not exposedto gaseous components.

The first electrode 43 in FIG. 21 resembles the first electrode 43 ofFIG. 15. Again, no ring portion is provided, but the center portion islayered comprising the getter material containing second layer 432continuously deposited on the first layer 431. However, as in theembodiment of FIG. 20, the second layer 432 additionally covers thesides of the first layer 431 and hence forms a cap for the first layer431 such that the first layer 431 is not exposed to gaseous components.

While above there are shown and described embodiments of the invention,it is to be understood that the invention is not limited thereto but maybe otherwise variously embodied and practiced within the scope of thefollowing claims.

What is claimed is:
 1. A sensor comprising a deformable membranedeflecting in response to a stimuli; and a capacitive element coupled tothe deformable membrane, wherein the capacitive element is disposedwithin an enclosed cavity of the sensor, and wherein the capacitiveelement changes capacitance in response to the deformable membranedeflecting, and wherein the capacitive element comprises a gettermaterial for collecting gas molecules within the enclosed cavity.
 2. Thesensor as described in claim 1, wherein the stimuli is externalpressure.
 3. The sensor as described in claim 1, wherein the enclosedcavity is formed by the deformable membrane, a dielectric material, anda semiconductor substrate.
 4. The sensor as described in claim 3,wherein the semiconductor substrate is a CMOS substrate.
 5. The sensoras described in claim 1, wherein the capacitive element comprises afirst electrode and a second electrode.
 6. The sensor as described inclaim 5, wherein the first electrode is disposed on a semiconductorsubstrate and comprises the getter material, and wherein the firstelectrode is fixed and immovable responsive to the stimuli.
 7. Thesensor as described in claim 5, wherein a material of the firstelectrode is selected from a group consisting of titanium, platinum, andzirconium.
 8. The sensor as described in claim 5, wherein the firstelectrode comprises a center portion and a ring portion around thecenter portion, wherein electrical connection is made through the centerportion, and wherein the ring portion comprises the getter material. 9.The sensor as described in claim 8, wherein the center portion comprisesa first layer overlaying a second layer, wherein the second layercomprises non-getter conducting material, and wherein the first layercomprises the getter material, and wherein the ring portion exclusivelycomprises the getter material.
 10. The sensor as described in claim 8,wherein the ring portion and the center portion comprise slots.
 11. Thesensor as described in claim 5, wherein the first electrode is ringshaped, and wherein the first electrode comprises a first layeroverlaying a second layer, wherein the second layer comprises non-getterconducting material, and wherein the first layer comprises the gettermaterial.
 12. The sensor as described in claim 5, wherein the firstelectrode comprises a plurality of elements, wherein neighboringelements of the plurality of elements are coupled to one another througha V-shaped bridge.
 13. The sensor as described in claim 5 furthercomprising a cavity, wherein the deformable membrane separates thecavity and a port open to an outside of the sensor, and wherein thefirst electrode is positioned at a bottom of the cavity facing thedeformable membrane.